public static ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
if (pHead1==null||pHead2==null) {
return null;
}
if (!isLoop(pHead1) && !isLoop(pHead2)) {
return getIntersectionNode(pHead1, pHead2);
}
if (isLoop(pHead1) && isLoop(pHead2)) {
ListNode loopNode1 = getLoopNode(pHead1);
ListNode loopNode2 = getLoopNode(pHead2);
if (loopNode1==loopNode2) {
return getIntersectionNode(pHead1, pHead2);
}
ListNode cur = loopNode1.next;
while (cur!=loopNode2) {
if (cur==loopNode1) {
return null;
}
cur = cur.next;
}
return cur;
}
return null;
}
public static ListNode getIntersectionNode(ListNode pHead1,ListNode pHead2) {
ListNode node1 = pHead1;
int nodeCount1 = 0;
ListNode node2 = pHead2;
int nodeCount2 = 0;
while (node1.next!=null) {
nodeCount1++;
node1 = node1.next;
}
while (node2.next!=null) {
nodeCount2++;
node2 = node2.next;
}
if (node1!=node2) {
return null;
}
int step = nodeCount1-nodeCount2;
if (step>0) {
while (step>0) {
step--;
pHead1 = pHead1.next;
}
} else {
step = -step;
while (step>0) {
step--;
pHead2 = pHead2.next;
}
}
while (pHead1!=pHead2) {
pHead1 = pHead1.next;
pHead2 = pHead2.next;
}
return pHead1;
}
public static boolean isLoop(ListNode node) {
if (node==null) {
return false;
}
if (node.next==null||node.next.next==null) {
return false;
}
ListNode fast = node.next.next;
ListNode slow = node.next;
while (fast.next!=null&&fast.next.next!=null) {
if (fast==slow) {
return true;
}
slow = slow.next;
fast = fast.next.next;
}
return false;
}
public static ListNode getLoopNode(ListNode node) {
ListNode fast = node.next.next;
ListNode slow = node.next;
while (fast!=slow) {
fast = fast.next.next;
slow = slow.next;
}
fast = node;
while (fast!=slow) {
fast = fast.next;
slow = slow.next;
}
return fast;
}
LinkedList:输入两个链表,找出它们的第一个公共结点。
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